Liquefied gas container

ABSTRACT

726,482. Heat insulation. GENERAL ELECTRIC CO. June 17, 1953 [July 11, 1952], No. 16752/53. Class 64 (2). A vessel for storing liquefied gas has outer and inner walls 10, 11 of metal, such as stainless steel, carbon steels electroplated or vitreous enamelled, or those metals known under the Registered Trade Marks &#34;Monel&#34; and &#34;Invar&#34;. Moreover, the evacuated space between these walls contains a blanket 13 of mineral fibres, e.g. slag wool, asbestos, aluminium oxide, glass or quartz, randomly orientated with their axes in planes generally perpendicular to the path of heat flow between the walls and preferably precompacted as described in Specification 715,175. Figures are given for the degree of vacuum, the density of the blanket and the diameter of the fibres. A further wall 14 divides the blanket 13 from a surface of the inner wall 11 which is made heat-reflecting like the surface of the wall 14 which faces it. The fibre blanket is made thicker for support of the inner wall where, as at 15, the wall 14 is interrupted. The tank, which may be spherical or cylindrical, has a filling and emptying pipe 19 extending through a bellows 16. A valve 21 permits periodical testing and evacuation of the insulation space.

3, 1957 H. M. STRONG ETAL LIQUEFIED GAS CONTAINER Filed July 11, 1952 Inventors: 'Herbert M-Strong, Francis F Bandy, 6.1 4 5M Their Attorney.

lUnit d S es Patent 2,776,776 LIQUEFIED GAS CONTAINER Herbert M. Strong and Francis P. Bundy, Schenectady,

N. Y., assignors to General Electric Company, a corporation of New York Application July 11, 1952, Serial No. 298,326

4 Claims. (Cl. 220-9) This invention relates to an insulated container for storing very cold liquefied gases such as methane, oxygen, natural gas and similar substances which must be cooled to an extremely low temperature in order to enable them to be stored at atmospheric pressure.

The storage of large quantities of very cold liquefied gases is of considerable importance in our present day technology. The efliciency and the economic value of such storage procedure depends heavily upon the evaporation losses resulting from heat leakage through the walls of the storage tank as well as upon the, cost and upkeep of the tank.

Storage tanks in current use forliquefied gas usually consist of double walled spherical or cylindrical tanks in which the space between the walls is filled with finely divided pottery materials such as kieselguhr, charcoal, and similar materials, and the space is evacuated to a rough vacuum of about 100 to 1000 microns Hg pressure. The weight of the inner tank and its contents is supported by tie rods or pads of material .different from the insulation filling material which extend between the inner and outer shells. The thickness of tthe insulating layer is usually 6 to 12 inches in the larger tanks and the average heat leakage rate with liquid methane, which boils at -161.5 C., at normal atmospheric air temperature outside is about 1-2 B. t. u. per hour per sq. ft. of

container area.

It is an object of this invention to provide a liquefied gas container in which the heat loss through the walls is of the order of 0.20.4 B. t. u. per hour per square foot of container area.

It is another object of the invention to provide a storage tank for liquefied gas wherein a comparatively thin blanket of mineral insulating fibers restricts the flow of heat through the container.

It is a further object of the invention to provide a liquefied gas container wherein radiationlosses are heldto a minimum by a pair of reflective surfaces interposed in the path of heat flow.

It is a still further object of tthe invention to provide a liquefied gas storage tank wherein heat losses are restricted by a combination of a pair of reflective surfaces and a blanket of mineral insulating fibers.

Briefly stated, in accordance with one aspect of this invention, a liquefied gas container comprises a doublewalled vessel having a gas-tight space of substantially uniform thickness between the walls, a blanket of mineral insulating fibers in the evacuated space, and a surface of high reflectivity in the space positioned in proximity to the inner wall, the outer surface of which is also highly reflective whereby the two reflective surfaces face each other.

Referring to the drawing, the container is seen to consist of a double-walled vessel having an outer tank 10 completely enclosing an inner tank 11 which is spaced a short distance from the outer tank 10 whereby the tanks define a space 12 of substantially uniform thickness. Connections between the tanks 10 and 11 are in gas-tight "ice relationship and the evacuated space 12 is maintained at a pressure of less than 1 mm. Hg and preferably at a pressure of less than 100 microns of Hg. We have found it possible to maintain a pressure as low as 1 micron Hg for a protracted period of time. There is no critical pressure level. Heat loss diminishes as pressure decreases. Accordingly, we prefer to maintain the pressure within the evacuated space 12 at the lowest feasible level.

The evacuated space 12 is occupied by a blanket 13 of mineral insulating fibers such as slag wool, asbestos, aluminum oxide, and siliceous materials such as glass fibers and quartz fibers. We prefer to use glass fibers in aceordance with the structure disclosed and claimed in our copending application, Serial No. 236,788, filed July 14, 1951, and assigned to the same assignee as the present application. In accordance with our copending application superior resistance to heat transfer is provided by a blanket of glass fibers randomly oriented with their axes in planes generally parallel to the plane of the nearest section of container wall. In other words, the axes are perpendicular totthe direction of heat transfer taking place through the container walls. We prefer to use glass fibers having a diameterof less than 0.001" and preferably of the order of 0.0002.

We prefer to precompact the" blanket of glass fibers in accordance with the method disclosed in Janos application Serial No. 236,971, filed'July 16, 1951, now abandoned, and assigned to the same assignee as the present application. In accordance with the Janos method we compress a blanket of glass fibers to a density of between 10 pounds and 30 pounds per cubic foot and heat them to atemperature just below thesoftening point of the glass while in this compressed condition. The blanket is then allowed to cool while in the compressed state. The subsequent release of the compression is then of little elfect as the fibers retain their compressed shape.

The blanket 13 of mineral fibers is positioned between the outer wall 10 and ametal surface 14 spaced in proximity to the wall of the inner-tank or container 11. The surface 14 is made highly reflecting on the side facing the wall of the inner tank 11 and the wall of the inner tank 11 facing the surface 14 is also made highly refleeting. The effect of these reflecting surfaces is to decrease the thermal radiation emissivity. The surface 14 may be a very thin metal sheet since it does not serve as a supporting member. It is desirable that it be as close as possible to the inner tank 11 while yet maintaining a slight distance apart therefrom. A distance of the order of 0.001 is desirable but in practice the distance is greater than this and not uniform over the entire surface.

Themetal surface 14 surrounds a major portion of inner tank 11 and is omitted around a portion of the bottom of the container structure indicated at 15. This omittedportion of surface 14 defines at least one open area adjacent the base of inner tank 11. In this section the blanket of mineral insulating fiber 13 is made slightly thicker so that it acts as a support for the inner tank 11.

A corrugated bellows 16 of thin metal of low thermal conductivity forms the pass-age between the inner tank and outer tank constituting the container. The bellows 16 terminates in a connecting ring 17 in which a plug 18 of material of low thermal conductivity is embedded. A

pipe 19 extends through the plug 18 and is utilized to introduce or remove liquid from the interior of the container.

For large installations an outlet 20 having a valve 21 is provided from the space 12 to which a vacuum pump (not shown) may be connected. In this way the container may be periodically tested and evacuated if necessary.

In the embodiment shown the container may be c011- :Howeven we, prefer to use metal'sjhaving a high resistance to corrosion as well as low thermal conductivity. The various stainless .steels, ,on -the market answer' this requirement admirably. Carbon steels maygbie used providedthey aregiven a t protective.coating such as vitreous enamel or an t electroplated tnetal to preyent the folrmation. ofirust. Alloys, such., as Monel metal, Invar and many others. are also satisfactory.

While,-the .present,invention has beendescribed with reference to particulanembodirnents thereof, it will be understood that numerous, modifications maybeymade by those skilled. in the-.artwithout actuallydeparting from the invention. Therefore,,we,aim in theappendedcl'ai ms to coverall such equivalent variations as come within the true spirit and scope of the foregoing disclosure.

What weclaim as new and desire to secure by Letters Patent of the United States is:

1. A liquefied gas container comprising an inner metal tank positioned within an outer metal tank, .said tank's being in spacedrelation-whereby there is an'evacuated space between the walls of said tanks, the surface of sjaid inner tank facing said evacuated space being highly reflective, ,a memberpositionedwithin said evacuated space and surrounding a major portion of said inner tank and defining at leastpneopen area. adjacent the base of said inner tank, said member being spaced fromjlsaid inner tank and said. outer tank and, having a highly reflective surface facing the highly reflective surface of saidinner tank, a blanket of clean, binder-freemineral.insulating fibers compacted to a density of more than 101poundsf'per cubicfoot positioned-adjacent; the inner surface of said outer tank and extending tosaid member .and to the inner Wall of said innertank in the region of. the area defined by said member,,said blanket constitutingajsupporting surface forsaid inner tank.

2. A liquefied gas container comprising an inner metal tank positioned within an.outer;metal tank, said tanks being in spaced relationwhereby there is, an evacu'ated space of substantiallymniform thickness between the walls m j r PQI B f s idi e ia k dfld fin ie a le one open area adjacentthe base of said inner" tank saidmember being spaced from said inner tank and said'outer tank and having wa highly. -reflective, surface facing the highly reflective surface of aid inner tank, a blanket of clean binder free mineral insula ting fibers, compacted to a density of. more than pounds per cubicffootposi t tioned adjacent theinner surface of said outer tank and ,.-extending towsaid member and to the inner wall of said inner tank in the region of the area defined by said mem- "ber, said'blanket "constituting a supporting surface for said inner tank.

3. A liquefied gas container comprising an inner metal tank positioned within an outer metal tank, said tanks being in spaced relation whereby there is an evacuated space between the walls ;of said tanks, the surface of said inner tankfacing said evacuated space being highly reflective, a member positionedwithint'said evacuated space and surrounding-a major portion of said inner tank and defining a't'ileast one open area adjacentthe base of said inner tank, said member being spaced from said innertank and saidouter tank and having a highly re fiective surface' facing the "highly reflective surface of said inner tank,f'a blanket of clean binder-free mineral insulating fibers compacted to a density of from 10 to 30 pounds per cubic foot positioned adjacent the inner surface of said outer tank and extending to said member and to" the inner wall ofsaid inner tank infthe region of the rea definfdby said member, said blanket constituting a siipporting surface for said inner tank.

'A liquefied'gas container comprtsmg an inner metal tank positioned within an outermetal tank,said tanks beinginspacedirelation whereby thcreis an evacuated space between the w'allsdf said tanks, the surface of'said jinnertanklfac'ing said evacuatedspace being highly'reflectivei a member positioned within said evacuated space and surrounding a major'por'tion of said inner tank and 'definingat"least bn' open area adjacent the base of said inner tank, said member beingspaced from said innentankfandi said 'outer tankand having a' highly reflective surface facing 'the highly reflective surface of said innertankjabtanketof clean, binder-free mineral insulatirig fibersicompacted to adensity of more than 10 pounds per cubic'foot positioned adjacent the inner surface of saidoutcr tank aridbxtending to said member and to Itheirin'erwaII offs aid inner tank in the region ofthe area gdefined'by said 'mfembergsaid fibers being randomly orieated with their ax'es' in planes generally perpendicular to the 'drection of heat flow through said blanket; said References Cited in the file of this patent UNITED STATES PATENTS ,-903,s7s ,Mock Nov. 17, 1908 -1 922,174 .Lyman May 18, .1909 1,463,027 Wile et al July 24, 1923 2,054,754 ,Kcllogg Sept. 15,1936 2,160,001 -Saborsky May.3Q, 1939 r 2,206,059 I Slayter July 2,1940 2,513,749 Shilling July 4, 1950 12,552,641 Morrison May 15,1951 2,610,757 Irvine Sept. 16,1952 2,643,021 1,. Freedman "June 23, 1953 2,643,487 Parker "June 30, 1953 jj aonnron PATENTS 409,113 France Apr. 26, 1934 Franc'e Sept. 17, 1934 lanket constituting 'a suppoiting surface for'said'inner 

1. A LIQUEFIED GAS CONTAINER COMPRISING AN INNER METAL TANK POSITIONED WITHIN AN OUTER METAL TANK, SAID TANKS BE ING IN SPACED RELATION WHEREBY THERE IS AN EVACUATED SPACE BETWEEN THE WALLS OF SAID TANKS, THE SURFACE OF SAID INNER TANK FACING SAID EVACUATED SPACE BEING HIGHLY REFLECTIVE, A MEMBER POSITIONED WITHIN SAID EVACUATED SPACE AND SURROUNDING A MOJOR PORTION OF SAID INNER TANK AND DEFINING AT LEAST ONE OPEN AREA ADJACENT THE BASE OF SAID INNER TANK, SAID MEMBER BEING SPACED FROM SAID INNER TANK AND SAID OUTER TANK AND HAVING A HIGHLY REFLECTIVE SURFACE FACING THE HIGHLY REFLECTIVE SURFACE OF SAID INNER TANK, A BLANKET OF CLEAN, BINDER-FREE MINERAL INSULATING 